&#34;null&#34; conical helix



Nov. 1, 1966 M. NUSSBAUM THE "NULL" CONICAL HELIX Filed Aug. 24, 1964 FIG. 4

FIG. 3

a. M S R w n TA N N R E5 m 5 Wu T IN A am- UT- N m M M W YiV B 4 M 8 8 United States Patent 3,283,332 NULL CONICAL HELIX Milton Nussbaum, Philadelphia, Pa., assignor to the United States of America as represented by the Secretary of the Army Filed Aug. 24, 1964, Ser. No. 392,373 2 Claims. (Cl. 343895) This invention relates to conical helix antennas, and more particularly to -a null conical helix antenna.

A new antenna, having utility in the field of radio direction finding, has been developed by modifying the standard double wound conical helix antenna. This new antenna has been named the null conical helix antenna.

Conical helix antennas, including the null conical helix antenna are characterized 'by frequency independent operation over a wide band width. Other characteristics of the null conical helix antenna are circular polarization, inherent sensing with no directional ambiguity, and extremely small pattern asymmetry (null tilt). It is the characteristic of inherent sensing without directional ambiguity that renders the null conical helix antenna especially useful in the field of radio direction finding.

Accordingly, it is an object of this invention to pro vide an antenna that has utility in the field of radio direction finding.

Another object of this invention is to provide an antenna that is characterized by frequency independent operation over a wide bandwidth, circular polarization, inherent sensing with no directional ambiguity, and extremely small pattern asymmetry.

The above mentioned and other objects will be evident from the following detailed description when read with the accompanying drawing wherein:

FIGURE 1 is a representation of a standard double wound conical helix antenna;

FIGURE 2 shows a typical radiation pattern of the standard double wound conical helix antenna;

FIGURE 3 is a representation of a null conical helix antenna.

FIGURE 4 shows a typical radiation pattern of a null conical helix antenna.

Referring now to FIGS. 1 and 2, the standard double wound conical helix antenna comprises two windings or arms 1 and 2. Each arm is wound to form a helix of diminishing diameter when going from the bottom to the top of the antenna. This type of winding gives an overall conical shape to the antenna. The arms can be made of rigid tubing so that the anus alone without any additional support constitute the antenna structure; or they can be made of flexible material wound on a nonconductive conical shaped form. The antenna can, of course, be fabricated in other ways than the two just mentioned. For example, the arms can be etched on a nonconductive conical shaped form.

The feed system to the conical helix antenna is a balanced system as is indicated by the numerals 3 and 4 in FIG. 1. This type of feed system gives rise to instantaneous currents, i and i of equal magnitude and opposing phase in each arm. However, the arms of the conical helix are wound in an opposite sense and this results in a second reversal of current direction to provide current moment addition along the cone axis. The additions of these current elements results in the radiation pattern 3,283,332 Patented Nov. 1, 1966 "ice shown in FIG. 2. The pattern shown in FIG. 2 in a unidirectional pattern off the apex of the cone.

The null conical helix antenna, shown in FIG. 2, is obtained by modifying the feed system of the standard double wound conical helix. The null conical helix has two arms or windings 4 and 5 wound in an opposite sense and can be fabricated in the manner described above. However, both arms 4 and 5 are fed from the center conductor 6 of a coax cable 8. The shield or outer conductor 7 of cable 8 is terminated in a loading disc or top hat 9 of optimum dimension. This type of feed system gives rises to instantaneous currents that produce opposing fields. The opposing fields produce an energy null along the axis of the cone, thereby giving rise to the type of radiation pattern shown in FIG. 4. Because of the axial symmetry of the helix, the three-dimensional radiation pattern is a figure of revolution, about the cone axis, of the two-dimen sional pattern shown in FIG. 4.

In addition to the difference in the feed systems, the null conical helix and the conical helix are distinguishable from one another by their relative sizes. If both antennas are designed to have the same optimum frequency of operation, the base diameter of the null conical helix will be twice the base diameter of the conical helix. This size differentiation becomes evident when one considers the contribution to the radiated field from the current elements. The vector addition results in a maximum field intensity along the cone axis for the conical helix when the winding circumference is equal to one wavelength, and provides maximum cancellation for the null conical helix when the winding circumference equals two wavelengths.

Many other variations and modifications of the invention will be apparent to those skilled in the art, therefore the specific example shown is to be considered as exemplary only and not as a limitation on the scope of the invention.

What is claimed is:

1. A null conical helix antenna comprising: a first con-ical helix wound in one direction; a second conical helix wound in a direction opposite the winding direction of said first conical helix, said first and second conical helices being coaxial; a coax cable having a center conductor and an outer shield, said cable being so positioned that its longitudinal axis coincides with the axis of said conical helices; means to connect said first and second conical helices to said center conductor; and a loading disc located at the apex of said conical helices and connected to said shield.

2. A null conical helix antenna comprising: a conical shaped nonconductive form; a first helix wound on said form in one direction; a second helix wound on said form in a direction opposite the winding of said first helix; a coax cable positioned along the axis of said form, said coax cable having a center conductor and an outer shield; means to connect said first and second helices to said center conductor; a loading disc positioned at the apex of said conical form; and means to connect said shield to said disc.

References Cited by the Examiner UNITED STATES PATENTS 2,919,442 12/ 1959 Nussbaum 343895 2,958,081 10/1961 Dyson 343895 3,188,643 6/ 1965 Dyson et a1. 343895 HERMAN KARL SAALBACH, Primary Examiner.

R. F. HUNT, Assistant Examiner. 

1. A NULL CONICAL HELIX ANTENNA COMPRISING: A FIRST CONICAL HELIX WOUND IN ONE DIRECTION; A SECOND CONICAL HELIXWOUND IN A DIRECTION OPPOSITE THE WINDING DIRECTION OF SAID FIRST CONICAL HELIX, SAID FIRST AND SECOND CONICAL HELICES BEING COAXIAL; A COAX CABLE HAVING A CENTER CONDUCTOR AND AN OUTER SHIELD, SAID CABLE BEING SO POSITIONED THAT ITS LONGITUDINAL AXIS COINCIDES WITH THE AXIS OF SAID CONICAL HELICES; MEANS TO CONNECT SAID FIRST AND SECOND CONICAL HELICES TO SAID CENTER CONDUCTOR; AND A LOADING DISCS LOCATED AT THE APEX OF SAID CONICAL HELICES AND CONNECTED TO SAID SHIELD. 